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Piscine Curiosities:
Strange Mating Rituals and Lifestyles

By Tammy Peluso

Birds do it, bees do it, even fishes in the sea do it; ever wonder how? Actually, fish have incredibly elaborate dating rituals that include choreographed mating dances, dramatic body signals and wild color changes. Each species has its own unique version of dinner, chocolate and flowers.

Many fish are spawners, they fertilize their eggs in open water; setting them adrift to fend for themselves in the open sea. Eggs typically have a bit of oil or buoyant fluid inside, which helps them float near the surface where they are less likely to be eaten. The eggs drift along with the tide through their larval stage; juveniles seek the shelter of a coral reef quickly after they are born. Although fish that spawn don't assist their young after conception, they do take measures to increase the eggs' chance of survival. Usually fish will spawn at times of the day when predation is lowest. Often they will migrate to the down-current edge of the reef to spawn, so their fertilized eggs will be carried swiftly to the safety of open water, away from the largest concentration of plankton-eating predators.

The nest builders are the easiest to watch. These fish perform intricate mating dances and lay their eggs in secluded crevices, in the sand or under ledges. The nests are nurtured and defended by one or both parents until the offspring has safely hatched. The easiest way to spot fish nests is to look for a frenzied cloud of reef fish, ravaging the reef. Quite often, buried beneath, you'll find the extremely agitated residents, valiantly defending their offspring.

Some of the most prolific and enthusiastic nest builders are Sergeant Majors, members of the genus Abudefduf; they are found on coral reefs in tropical oceans, worldwide. Sergeant Majors can be seen creating and guarding their nests in the spring and summer; they go through a series of month long cycles. The male of this species builds the nest and maintains it. During the courting period the male's body darkens into a deep royal blue, obscuring the five vertical black bars. The males entice passing females to deposit eggs into their nests by performing showy zigzag swimming patterns. The males will court many females during this period and can accumulate more than 200,000 eggs, creating a beautiful fuchsia-colored egg carpet. It only takes four days for the eggs to mature; during this period the male regains his normal coloration. When the eggs hatch the tiny fish seek shelter on the reef and the male rejoins the general Sergeant Major population, awaiting the start of the next breeding cycle.

Clownfish, common throughout the Pacific, are one of the few fish species that are monogamous and mate for life. Clownfish are always found living within the sheltered protection of anemones; flower-like animals with velvety stinging tentacles. A thick coating of mucus covers the body of the clownfish, giving it immunity from the anemone's deadly sting; the anemone give the clownfish protection from predators. These nest builders deposit their eggs on the hard substrate that the anemone is attached to, creating a very safe haven for their offspring. Anemones typically eat fish, shrimp, crinoids and other small animals, which they capture with their stinging tentacles and digest in their central body cavity. There are usually plenty of leftovers, so free meals are an added benefit for the clownfish. Both parties benefit from this symbiotic relationship. The tiny clownfish is as fearless as a grizzly bear and helps the anemone by chasing away would-be predators.

Nature has developed extraordinary ways of ensuring survival of each species. Many species of fish, including clownfish, parrotfish, Anthias, wrasses, groupers and some angelfish are hermaphrodites, which means they have the ability to change their sex after they are born. A few species, such as hamlets, the Belted Sandfish and the Caribbean Harlequin Bass are simultaneous hermaphrodites; they have the unique ability to change sex at will throughout their lives. Most hermaphrodites are sequential, which means they begin life as a male or female and change sex when a need in the community arises. Quite often drastic color and pattern changes will accompany the transformation.

The largest clownfish living in an anemone is always a female; there is usually one male and occasionally a few juveniles. The males are extremely territorial and will not allow another mature male to live within the same anemone. All young clownfish mature as males so when they reach maturity they are evicted and forced to find an anemone of their own. If something happens to the female before the juveniles mature then the large male will change into a female and the largest juvenile will grow quickly and assume the position of the dominant male. The growth of the smaller clownfish will often be stunted until one of the larger fish disappears.

Another interesting hermaphrodite is the dazzling neon Blue Ribbon Eel (Rhinomuraena quaesita), common on reefs throughout the Indo-Pacific. This is the only species of moray that has the ability to change sex. All juvenile Ribbon Eels are black; they remain male as they mature, developing golden fins and their unusual blue color. Once mature, the Ribbon Eel can change into a female if the need arises. Moray eels are pelagic spawners and their offspring have a lengthy larval stage, explaining the abundance of morays on coral reefs and their wide distribution.

Although some species, such as wrasses and parrotfish, spawn at midday, the majority of reef fish perform their mating rituals at dusk and dawn, when pelagic predators are resting. Driven by instinct to ensure the survival of their species, they risk exposure to their own enemies in order to protect their progeny. The 'dating game' is just one of the reef's countless curiosities.